1. Field of the Invention
The present invention relates to a method of manufacturing a stator winding of a rotary electric machine such as a vehicle ac generator to be mounted in a passenger car or a truck.
2. Description of the Related Art
A demand for increasing the output power of a vehicle ac generator has increased as electric load for safety devices is increasing in recent years. In order to meet such a demand, JP-A-2000-350423 proposes “a method of manufacturing a stator winding of a rotary electric machine” which aims to increase the output power by mounting regularly formed U-shaped conductor segments of high density in each slot of a stator core. In this method of manufacturing a stator winding, there is a step for bending U-shaped conductor segments that are inserted into slots by a twisting device, thereby increasing manufacturing speed.
In a stator winding manufactured by this method of manufacturing, lead-specialized U-shaped conductor segments are included besides two kinds of medium U-shaped conductor segments. The lead-specialized U-shaped conductor segments connect the stator winding and the neutral point of Y-connected winding to a rectifier and, therefore, are formed to be longer than the medium U-shaped conductor segments.
The U-shaped conductor segments, each of a pair of straight portions is disposed in a radial direction and is bent in a circumferential direction so that one inclines to a direction opposite to the other at a step of twisting before inserting straight portions of the conductor segments into slots. This step of twisting is carried out by turning an inner ring-shaped tool and an outer ring-shaped tool in opposite circumferential directions while pressing the turn portions of the U-shaped conductor segments that are inserted into through holes formed at the same circumferential pitches of the inner ring-shaped tool and the outer ring-shaped tool by a pressing tool. In the twisting step, the inner and outer ring-shaped tools respectively turn in the opposite circumferential directions while the turn portions of the respective U-shaped conductor segments that are inserted in the through holes of the inner and outer ring-shaped tools are pressed by the pressing tool. Thus, the stator winding is manufactured through various steps after the preformed U-shaped conductor segments are inserted into respective slots of a stator core.
In the method disclosed in the above publication JP-A-2000-350423, besides two kinds of medium U-shaped conductor segments that compose phase coils of a stator winding, lead-specialized U-shaped conductor segments that form lead wires of the respective phase coils are used. Because the lead-specialized U-shaped conductor is longer than the other U-shaped conductor segments, the pressing tool for pressing the turn portions has recesses into which the lead-specialized shape conductor segments are inserted when the straight portions of the respective U-shaped conductor segments are twisted.
In the ac generator disclosed in the above publication JP-A-2000-350423, two leads extending from one of the lead-specialized U-shaped conductor segments are disposed at approximately the same circumferential position of the stator core. Therefore, the through holes of the pressing tool for the medium U-shaped conductor segments have rectangular shape with the longer sides being in parallel to the radial direction.
If a change to the specification of the stator winding is made, two lead wires that are made up of one of the lead-specialized U-shaped conductor segments are not always extended from the same circumferential position and may be extended from different circumferential positions. Therefore, the recesses of the pressing tool for the lead-specialized U-shaped conductor segments are expanded in the circumferential directions, resulting in that the turn portions of the other U-shaped conductor segments disposed in the recesses can not be restrained in the axial direction.